Disable Impeller when the manifest explicitly disables it (#53108)

After https://github.com/flutter/engine/pull/53099, impeller is always enabled, even if the manifest disables it using `io.flutter.embedding.android.EnableImpeller`. 

This PR causes it to respect the manifest value if it is explicitly disabled.

Fixes b/343603270

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

diff --git a/shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java b/shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java
index b540c20..c720f37 100644
--- a/shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java
+++ b/shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java
@@ -340,8 +340,10 @@
       shellArgs.add("--prefetched-default-font-manager");
 
       if (metaData != null) {
-        if (metaData.getBoolean(ENABLE_IMPELLER_META_DATA_KEY, false)) {
+        if (metaData.getBoolean(ENABLE_IMPELLER_META_DATA_KEY, true)) {
           shellArgs.add("--enable-impeller");
+        } else {
+          shellArgs.add("--enable-impeller=false");
         }
         if (metaData.getBoolean(ENABLE_VULKAN_VALIDATION_META_DATA_KEY, false)) {
           shellArgs.add("--enable-vulkan-validation");